Sheet buffering system

ABSTRACT

The present disclosure provides a printing device comprising a sheet buffer including a paper path having a plurality of nip pairs for selectively receiving and releasing a plurality of printer sheets. The plurality of nip pairs include a fixed load nip pair, a fixed unload nip pair, and at least another intermediate fixed nip pair therebetween. In a first operation each subsequent sheet of the plurality of sheets is shingled over a previous sheet wherein the plurality of sheets can be stopped in the intermediate nip pair or pairs. Individual sheets of the plurality of sheets can be advanced to the unload nip pair sequentially in a second operation whereupon the individual sheets are successively unloaded as needed in a first in first out order.

BACKGROUND

The present disclosure provides for an apparatus in conjunction with aplurality of image marking engines or image recording apparatusesproviding a multifunctional and expandable printing system. It findsparticular application in conjunction with integrated printing modulesconsisting of several marking engines, each having the same or differentprinting capabilities, and will be described with particular referencethereto. However, it is to be appreciated that the present exemplaryembodiments are also amenable to other like applications.

Various apparatuses for recording images on sheets have heretofore beenput into practical use. For example, there are copying apparatuses ofthe type in which the images of originals are recorded on sheets througha photosensitive medium or the like, and printers in which imageinformation transformed into an electrical signal is reproduced as animage on a sheet by an impact system (the type system, the wire dotsystem or the like) or a non-impact system (the thermosensitive system,the ink jet system, the laser beam system or the like).

The marking engine of an electronic reprographic printing system isfrequently an electrophotographic printing machine. In such a machine, aphotoconductive belt is charged to a substantially uniform potential tosensitize the belt surface. The charged portion of the belt isthereafter selectively exposed. Exposure of the charged photoconductivebelt or member dissipates the charge thereon in the irradiated areas.Thisrecords an electrostatic latent image on the photoconductive membercorresponding to the informational areas contained within the originaldocument being reproduced. After the electrostatic latent image isrecorded on the photoconductive member, the latent image on thephotoconductive member is subsequently transferred to a copy sheet. Thecopy sheet is heated to permanently affix the toner image thereto inimage configuration.

Multi-color electrophotographic printing is substantially identical tothe foregoing process of black and white printing. However, rather thanforming a single latent image on the photoconductive surface, successivelatent images corresponding to different colors are recorded thereon.Each single color electrostatic latent image is developed with toner ofa color complementary thereto. This process is repeated a plurality ofcycles for differently colored images and their respectivecomplementarily colored toner. Each single color toner image istransferred to the copy sheet in superimposed registration with theprior toner image. This creates a multi-layered toner image on the copysheet. Thereafter, the multi-layered toner image is permanently affixedto the copy sheet creating a color copy. The developer material may be aliquid or a powder material.

In the process of black and white printing, the copy sheet is advancedfrom an input tray to a path internal the electrophotographic printingmachine where a toner image is transferred thereto and then to an outputcatch tray for subsequent removal therefrom by the machine operator. Inthe process of multi-color printing, the copy sheet moves from an inputtray through a recirculating path internal the printing machine where aplurality of toner images is transferred thereto and then to an outputcatch tray for subsequent removal. With regard to multi-color printing,as one example, a sheet gripper secured to a transport receives the copysheet and transports it in a recirculating path enabling the pluralityof different color images to be transferred thereto. The sheet grippergrips one edge of the copy sheet and moves the sheet in a recirculatingpath so that accurate multi-pass color registration is achieved. In thisway, magenta, cyan, yellow, and black toner images are transferred tothe copy sheet in registration with one another.

The present disclosure is directed to the art of paper sheet handlingand, more particularly, to a sheet buffering system. The disclosure isespecially suited for use in the paper handling and transport systems ofelectrophotographic printing machines and will be described withreference thereto; however, as will become apparent, the disclosurecould be used in many types of paper sheet handling systems in a varietyof different machines.

In electrophotographic printing machines, it is sometimes necessary ordesirable to temporarily hold or delay the transport of individual papersheets at various times in the processor to provide additional time fordownstream processing to be performed. Such temporary holding ordelaying of sheets is generally referred to as “buffering” and has beenaccomplished in many different ways. One prior art method of bufferinghas been to temporarily slow or stop a roll nip or other paper transportfor a period of time equal to the inter-copy-gap between successivesheets. Of course, this yields only a very short buffering time. Iflonger times are required, other systems must be used. For example,multiple path systems and systems which run sheets against stalled rollpairs or stop gates have sometimes been used.

In printing a job matrix requiring, for example, both monochrome andcolor mixed prints, the monochrome printer would be forced to reduce itsproductivity if several color prints were sequentially required in thejob matrix. The color engine, if required to print on demand by matrixorientation may be forced to continually cycle up and down numeroustimes if the majority of the matrix was only monochrome with colorinserts. Single print output is not very efficient and wastes supplies.

In multiple integrated print engine applications, different printengines can be combined for various output applications. For example,relatively fast monochrome engines combined with much slower colorengines. This disclosure relates to a document handling system forprinting systems in which a set of individual documents may be mergedfrom multiple print engines into a single job matrix. This allows, forexample, slower color print images to be printed sequentially in advanceand delivered into the print job matrix when needed.

U.S. Pat. No. 5,383,656 to Mandel et. al. and U.S. Pat. No. 4,093,372 toGuenther are incorporated by reference as background information.

The following patents/applications, the disclosures of each beingtotally incorporated herein by reference are mentioned:

U.S. Publication No. US-2006-0114497-A1 (Attorney Docket No.20031830-US-NP), Published Jun. 1, 2006, entitled “PRINTING SYSTEM,” byDavid G. Anderson, et al., and claiming priority to U.S. ProvisionalApplication Ser. No. 60/631,651, filed Nov. 30, 2004, entitled “TIGHTLYINTEGRATED PARALLEL PRINTING ARCHITECTURE MAKING USE OF COMBINED COLORAND MONOCHROME ENGINES”;

U.S. Publication No. US-2006-0067756-A1 (Attorney Docket No.20031867Q-US-NP), filed Sep. 27, 2005, entitled “PRINTING SYSTEM,” byDavid G. Anderson, et al., and claiming priority to U.S. ProvisionalPatent Application Ser. No. 60/631,918 (Attorney Docket No.20031867-US-PSP), filed Nov. 30, 2004, entitled “PRINTING SYSTEM WITHMULTIPLE OPERATIONS FOR FINAL APPEARANCE AND PERMANENCE,” and U.S.Provisional Patent Application Ser. No. 60/631,921, filed Nov. 30, 2004,entitled “PRINTING SYSTEM WITH MULTIPLE OPERATIONS FOR FINAL APPEARANCEAND PERMANENCE”;

U.S. Publication No. US-2006-0067757-A1 (Attorney Docket No.20031867Q-US-NP), filed Sep. 27, 2005, entitled “PRINTING SYSTEM,” byDavid G. Anderson, et al., and claiming priority to U.S. ProvisionalPatent Application Ser. No. 60/631,918, Filed Nov. 30, 2004, entitled“PRINTING SYSTEM WITH MULTIPLE OPERATIONS FOR FINAL APPEARANCE ANDPERMANENCE,” and U.S. Provisional Patent Application Ser. No.60/631,921, filed Nov. 30, 2004, entitled “PRINTING SYSTEM WITH MULTIPLEOPERATIONS FOR FINAL APPEARANCE AND PERMANENCE”;

U.S. Pat. No. 6,973,286 (Attorney Docket A2423-US-NP), issued Dec. 6,2005, entitled “HIGH RATE PRINT MERGING AND FINISHING SYSTEM FORPARALLEL PRINTING,” by Barry P. Mandel, et al.;

U.S. application Ser. No. 10/785,211 (Attorney Docket A3249P1-US-NP),filed Feb. 24, 2004, entitled “UNIVERSAL FLEXIBLE PLURAL PRINTER TOPLURAL FINISHER SHEET INTEGRATION SYSTEM,” by Robert M. Lofthus, et al.;

U.S. Application No. US-2006-0012102-A1 (Attorney Docket A0723-US-NP),published Jan. 19, 2006, entitled “FLEXIBLE PAPER PATH USINGMULTIDIRECTIONAL PATH MODULES,” by Daniel G. Bobrow;

U.S. application Ser. No. 10/917,676 (Attorney Docket A3404-US-NP),filed Aug. 13, 2004, entitled “MULTIPLE OBJECT SOURCES CONTROLLED AND/ORSELECTED BASED ON A COMMON SENSOR,” by Robert M. Lofthus, et al.;

U.S. Publication No. US-2006-0033771-A1 (Attorney Docket20040184-US-NP), published Feb. 16, 2006, entitled “PARALLEL PRINTINGARCHITECTURE CONSISTING OF CONTAINERIZED IMAGE MARKING ENGINES AND MEDIAFEEDER MODULES,” by Robert M. Lofthus, et al.;

U.S. Pat. No. 7,924,152 (Attorney Docket A4050-US-NP), issued Apr. 4,2006, entitled “PRINTING SYSTEM WITH HORIZONTAL HIGHWAY AND SINGLE PASSDUPLEX,” by Robert M. Lofthus, et al.;

U.S. Publication No. US-2006-0039728-A1 (Attorney Docket A3190-US-NP),published Feb. 23, 2006, entitled “PRINTING SYSTEM WITH INVERTERDISPOSED FOR MEDIA VELOCITY BUFFERING AND REGISTRATION,” by Joannes N.M. dejong, et al.;

U.S. application Ser. No. 10/924,458 (Attorney Docket A3548-US-NP),filed Aug. 23, 2004, entitled “PRINT SEQUENCE SCHEDULING FORRELIABILITY,” by Robert M. Lofthus, et al.;

U.S. Publication No. US-2006-0039729-A1 (Attorney Docket No.A3419-US-NP), published Feb. 23, 2006, entitled “PARALLEL PRINTINGARCHITECTURE USING IMAGE MARKING ENGINE MODULES (as amended),” by BarryP. Mandel, et al.;

U.S. Pat. No. 6,959,165 (Attorney Docket A2423-US-DIV), issued Oct. 25,2005, entitled “HIGH RATE PRINT MERGING AND FINISHING SYSTEM FORPARALLEL PRINTING,” by Barry P. Mandel, et al.;

U.S. application Ser. No. 10/933,556 (Attorney Docket No. A3405-US-NP),filed Sep. 3, 2004, entitled “SUBSTRATE INVERTER SYSTEMS AND METHODS,”by Stan A. Spencer, et al.;

U.S. application Ser. No. 10/953,953 (Attorney Docket No. A3546-US-NP),filed Sep. 29, 2004, entitled “CUSTOMIZED SET POINT CONTROL FOR OUTPUTSTABILITY IN A TIPP ARCHITECTURE,” by Charles A. Radulski, et al.;

U.S. Publication No. US-2006-0115284-A1 (Attorney Docket20040314-US-NP), Published Jun. 1, 2006, entitled “SEMI-AUTOMATIC IMAGEQUALITY ADJUSTMENT FOR MULTIPLE MARKING ENGINE SYSTEMS,” by Robert E.Grace, et al.;

U.S. application Ser. No. 10/999,450 (Attorney Docket No.20040985-US-NP), filed Nov. 30, 2004, entitled “ADDRESSABLE FUSING FORAN INTEGRATED PRINTING SYSTEM,” by Robert M. Lofthus, et al.;

U.S. Publication No. US-2006-0115287-A1 (Attorney Docket No.20040503-US-NP), Published Jun. 1, 2006, entitled “GLOSSING SYSTEM FORUSE IN A TIPP ARCHITECTURE,” by Bryan J. Roof;

U.S. application Ser. No. 11/000,168 (Attorney Docket No.20021985-US-NP), filed Nov. 30, 2004, entitled “ADDRESSABLE FUSING ANDHEATING METHODS AND APPARATUS,” by David K. Biegelsen, et al.;

U.S. Publication No. US-2006-0115288-A1 (Attorney Docket No.20040503Q-US-NP), Published Jun. 1, 2006, entitled “GLOSSING SYSTEM FORUSE IN A TIPP ARCHITECTURE,” by Bryan J. Roof;

U.S. Pat. No. 6,925,283 (Attorney Docket A2423-US-DIV1), issued Aug. 2,2005, entitled “HIGH PRINT RATE MERGING AND FINISHING SYSTEM FORPARALLEL PRINTING,” by Barry P. Mandel, et al.;

U.S. Publication No. US-2006-0176336-A1 (Attorney Docket20040447-US-NP), Published Aug. 10, 2006, entitled “PRINTING SYSTEMS,”by Steven R. Moore, et al.;

U.S. Publication No. US-2006-0132815-A1 (Attorney Docket20040744-US-NP), Published Jun. 22, 2006, entitled “PRINTING SYSTEMS,”by Robert M. Lofthus, et al.;

U.S. Publication No. US-2006-0197966-A1 (Attorney Docket20031659-US-NP), Published Sep. 7, 2006, entitled “GRAY BALANCE FOR APRINTING SYSTEM OF MULTIPLE MARKING ENGINES,” by R. Enrique Viturro, etal.;

U.S. Publication No. US-2006-0114313-A1 (Attorney Docket20040448-US-NP), Published Jun. 1, 2006, entitled “PRINTING SYSTEM,” bySteven R. Moore;

U.S. application Ser. No. 11/084,280 (Attorney Docket 20040974-US-NP),filed Mar. 18, 2005, entitled “SYSTEMS AND METHODS FOR MEASURINGUNIFORMITY IN IMAGES,” by Howard Mizes;

U.S. application Ser. No. 11/089,854 (Attorney Docket 20040241-US-NP),filed Mar. 25, 2005, entitled “SHEET REGISTRATION WITHIN A MEDIAINVERTER,” by Robert A. Clark, et al.;

U.S. application Ser. No. 11/090,498 (Attorney Docket 20040619-US-NP),filed Mar. 25, 2005, entitled “INVERTER WITH RETURN/BYPASS PAPER PATH,”by Robert A. Clark;

U.S. application Ser. No. 11/090,502 (Attorney Docket 20031468-US-NP),filed Mar. 25, 2005, entitled IMAGE QUALITY CONTROL METHOD AND APPARATUSFOR MULTIPLE MARKING ENGINE SYSTEMS,” by Michael C. Mongeon;

U.S. application Ser. No. 11/093,229 (Attorney Docket 20040677-US-NP),filed Mar. 29, 2005, entitled “PRINTING SYSTEM,” by Paul C. Julien;

U.S. application Ser. No. 11/095,872 (Attorney Docket 20040676-US-NP),filed Mar. 31, 2005, entitled “PRINTING SYSTEM,” by Paul C. Julien;

U.S. application Ser. No. 11/094,864 (Attorney Docket 20040971-US-NP),filed Mar. 31, 2005, entitled “PRINTING SYSTEM,” by Jeremy C. deJong, etal.;

U.S. application Ser. No. 11/095,378 (Attorney Docket 20040446-US-NP),filed Mar. 31, 2005, entitled “IMAGE ON PAPER REGISTRATION ALIGNMENT,”by Steven R. Moore, et al.;

U.S. application Ser. No. 11/094,998 (Attorney Docket 20031520-US-NP),filed Mar. 31, 2005, entitled “PARALLEL PRINTING ARCHITECTURE WITHPARALLEL HORIZONTAL PRINTING MODULES,” by Steven R. Moore, et al.;

U.S. application Ser. No. 11/102,899 (Attorney Docket 20041209-US-NP),filed Apr. 8, 2005, entitled “SYNCHRONIZATION IN A DISTRIBUTED SYSTEM,”by Lara S. Crawford, et al.;

U.S. application Ser. No. 11/102,910 (Attorney Docket 20041210-US-NP),filed Apr. 8, 2005, entitled “COORDINATION IN A DISTRIBUTED SYSTEM,” byLara S. Crawford, et al.;

U.S. application Ser. No. 11/102,355 (Attorney Docket 20041213-US-NP),filed Apr. 8, 2005, entitled “COMMUNICATION IN A DISTRIBUTED SYSTEM,” byMarkus P. J. Fromherz, et al.;

U.S. application Ser. No. 11/102,332 (Attorney Docket 20041214-US-NP),filed Apr. 8, 2005, entitled “ON-THE-FLY STATE SYNCHRONIZATION IN ADISTRIBUTED SYSTEM,” by Haitham A. Hindi;

U.S. application Ser. No. 11/109,558 (Attorney Docket 19971059-US-NP),filed Apr. 19, 2005, entitled “SYSTEMS AND METHODS FOR REDUCING IMAGEREGISTRATION ERRORS,” by Michael R. Furst, et al.;

U.S. application Ser. No. 11/109,566 (Attorney Docket 20032019-US-NP),filed Apr. 19, 2005, entitled “MEDIA TRANSPORT SYSTEM,” by Barry P.Mandel, et al.;

U.S. application Ser. No. 11/109,996 (Attorney Docket 20040704-US-NP),filed Apr. 20, 2005, entitled “PRINTING SYSTEMS,” by Michael C. Mongeon,et al.;

U.S. application Ser. No. 11/115,766 (Attorney Docket 20040656-US-NP,Filed Apr. 27, 2005, entitled “IMAGE QUALITY ADJUSTMENT METHOD ANDSYSTEM,” by Robert E. Grace;

U.S. application Ser. No. 11/122,420 (Attorney Docket 20041149-US-NP),filed May. 5, 2005, entitled “PRINTING SYSTEM AND SCHEDULING METHOD,” byAustin L. Richards;

U.S. application Ser. No. 11/136,959 (Attorney Docket 20040649-US-NP),filed May. 25, 2005, entitled “PRINTING SYSTEMS,” by Kristine A. German,et al.;

U.S. application Ser. No. 11/137,634 (Attorney Docket 20050281-US-NP),filed May. 25, 2005, entitled “PRINTING SYSTEM,” by Robert M. Lofthus,et al.;

U.S. application Ser. No. 11/137,251 (Attorney Docket 20050382-US-NP),filed May. 25, 2005, entitled “SCHEDULING SYSTEM,” by Robert M. Lofthus,et al.;

U.S. Publication No. US-2006-0066885-A1 (Attorney Docket A3546-US-CIP),filed May. 25, 2005, entitled “PRINTING SYSTEM,” by David G. Anderson,et al.;

U.S. application Ser. No. 11/143,818 (Attorney Docket 200400621-US-NP),filed Jun. 2, 2005, entitled “INTER-SEPARATION DECORRELATOR,” by Edul N.Dalal, et al.;

U.S. application Ser. No. 11/146,665 (Attorney Docket 20041296-US-NP),filed Jun. 7, 2005, entitled “LOW COST ADJUSTMENT METHOD FOR PRINTINGSYSTEMS,” by Michael C. Mongeon;

U.S. application Ser. No. 11/152,275 (Attorney Docket 20040506-US-NP),filed Jun. 14, 2005, entitled “WARM-UP OF MULTIPLE INTEGRATED MARKINGENGINES,” by Bryan J. Roof, et al.;

U.S. application Ser. No. 11/156,778 (Attorney Docket 20040573-US-NP),filed Jun. 20, 2005, entitled “PRINTING PLATFORM,” by Joseph A. Swift;

U.S. application Ser. No. 11/157,598 (Attorney Docket 20041435-US-NP),filed Jun. 21, 2005, entitled “METHOD OF ORDERING JOB QUEUE OF MARKINGSYSTEMS,” by Neil A. Frankel;

U.S. application Ser. No. 11/166,460 (Attorney Docket 20040505-US-NP),filed Jun. 24, 2005, entitled “GLOSSING SUBSYSTEM FOR A PRINTINGDEVICE,” by Bryan J. Roof, et al.;

U.S. application Ser. No. 11/166,581 (Attorney Docket 20040812-US-NP),filed Jun. 24, 2005, entitled “MIXED OUTPUT PRINT CONTROL METHOD ANDSYSTEM,” by Joseph H. Lang, et al.;

U.S. application Ser. No. 11/166,299 (Attorney Docket 20041110-US-NP),filed Jun. 24, 2005, entitled “PRINTING SYSTEM,” by Steven R. Moore;

U.S. application Ser. No. 11/170,975 (Attorney Docket 20040983-US-NP),filed Jun. 30, 2005, entitled “METHOD AND SYSTEM FOR PROCESSING SCANNEDPATCHES FOR USE IN IMAGING DEVICE CALIBRATION,” by R. Victor Klassen;

U.S. application Ser. No. 11/170,873 (Attorney Docket 20040964-US-NP),filed Jun. 30, 2005, entitled “COLOR CHARACTERIZATION OR CALIBRATIONTARGETS WITH NOISE-DEPENDENT PATCH SIZE OR NUMBER,” by R. VictorKlassen;

U.S. application Ser. No. 11/170,845 (Attorney Docket 20040186-US-NP),filed Jun. 30, 2005, entitled “HIGH AVAILABILITY PRINTING SYSTEMS,” byMeera Sampath, et al.;

U.S. application Ser. No. 11/189,371 (Attorney Docket 20041111-US-NP),filed Jul. 26, 2005, entitled “PRINTING SYSTEM,” by Steven R. Moore, etal.;

U.S. application Ser. No. 11/208,871 (Attorney Docket 20041093-US-NP),filed Aug. 22,2005, entitled “MODULAR MARKING ARCHITECTURE FOR WIDEMEDIA PRINTING PLATFORM,” by Edul N. Dalal, et al.;

U.S. application Ser. No. 11/215,791 (Attorney Docket 2005077-US-NP),filed Aug. 30, 2005, entitled “CONSUMABLE SELECTION IN A PRINTINGSYSTEM,” by Eric Hamby, et al.;

U.S. application Ser. No. 11/222,260 (Attorney Docket 20041220-US-NP),filed Sep. 8, 2005, entitled “METHOD AND SYSTEMS FOR DETERMINING BANDINGCOMPENSATION PARAMETERS IN PRINTING SYSTEMS,” by Goodman, et al.;

U.S. application Ser. No. 11/234,553 (Attorney Docket 20050371-US-NP),filed Sep. 23, 2005, entitled “MAXIMUM GAMUT STRATEGY FOR THE PRINTINGSYSTEMS,” by Michael C. Mongeon;

U.S. application Ser. No. 11/234,468 (Attorney Docket 20050262-US-NP),filed Sep. 23, 2005, entitled “PRINTING SYSTEM,” by Eric Hamby, et al.;

U.S. application Ser. No. 11/247,778 (Attorney Docket 20031549-US-NP),filed Oct. 11, 2005, entitled “PRINTING SYSTEM WITH BALANCED CONSUMABLEUSAGE,” by Charles Radulski, et al.;

U.S. application Ser. No. 11/248,044 (Attorney Docket 20050303-US-NP),filed Oct. 12, 2005, entitled “MEDIA PATH CROSSOVER FOR PRINTINGSYSTEM,” by Stan A. Spencer, et al.; and

U.S. application Ser. No. 11/274,638 (Attorney Docket 20050689-US-NP),filed Nov. 15, 2005, entitled “GAMUT SELECTION IN MULTI-ENGINE SYSTEMS,”by Wencheng Wu, et al.;

U.S. application Ser. No. 11/287,177 (Attorney Docket 20050909-US-NP),filed Nov. 23, 2005, entitled “MEDIA PASS THROUGH MODE FOR MULTI-ENGINESYSTEM,” by Barry P. Mandel, et al.;

U.S. application Ser. No. 11/287,685 (Attorney Docket 20050363-US-NP),filed Nov. 28, 2005, entitled “MULTIPLE IOT PPHOTORECEPTOR BELT SEAMSYNCHRONIZATION,” by Kevin M. Carolan;

U.S. application Ser. No. 11/291,860 (Attorney Docket 20050966-US-NP),filed Nov. 30, 2005, entitled “MEDIA PATH CROSSOVER CLEARANCE FORPRINTING SYSTEM,” by Keith L. Willis;

U.S. application Ser. No. 11/292,388 (Attorney Docket 20051103-US-NP),filed Nov. 30. 2005, entitled “PRINTING SYSTEM,” by David A. Mueller;

U.S. application Ser. No. 11/292,163 (Attorney Docket 20050489-US-NP),filed Nov. 30, 2005, entitled “RADIAL MERGE MODULE FOR PRINTING SYSTEM,”by Barry P. Mandel, et al.;

U.S. application Ser. No. 11/291,583 (Attorney Docket 20041755-US-NP),filed Nov. 30, 2005, entitled “MIXED OUTPUT PRINTING SYSTEM,” by JosephH. Lang;

U.S. application Ser. No. 11/312,081 (Attorney Docket 20050330-US-NP),filed Dec. 20, 2005, entitled “PRINTING SYSTEM ARCHITECTURE WITH CENTERCROSS-OVER AND INTERPOSER BY-PASS PATH,” by Barry P. Mandel, et al.;

U.S. application Ser. No. 11/314,828 (Attorney Docket 20051171-US-NP),filed Dec. 21, 2005, entitled “MEDIA PATH DIAGNOSTICS WITH HYPER MODULEELEMENTS,” by David G. Anderson, et al;

U.S. application Ser. No. 11/314,774 (Attorney Docket 20050137-US-NP),filed Dec. 21, 2005, entitled “METHOD AND APPARATUS FOR MULTIPLE PRINTERCALIBRATION USING COMPROMISE AIM,” by R. Victor Klassen;

U.S. application Ser. No. 11/317,589 (Attorney Docket 20040327-US-NP),filed Dec. 23, 2005, entitled “UNIVERSAL VARIABLE PITCH INTERFACEINTERCONNECTING FIXED PITCH SHEET PROCESSING MACHINES,” by David K.Biegelsen, et al.;

U.S. application Ser. No. 11/317,167 (Attorney Docket 20050823-US-NP),filed Dec. 23, 2005, entitled “PRINTING SYSTEM,” by Robert M. Lofthus,et al.;

U.S. application Ser. No. 11/331,627 (Attorney Docket 20040445-US-NP),filed 01-13-06, entitled “PRINTING SYSTEM INVERTER APPARATUS”, by StevenR. Moore;

U.S. application Ser. No. 11/341,733 (Attorney Docket 20041543-US-NP),filed Jan. 27, 2006, entitled “PRINTING SYSTEM AND BOTTLENECKOBVIATION”, by Kristine A. German;

U.S. application Ser. No. 11/349,828 (Attorney Docket 20051118-US-NP),filed Feb. 8,2005, entitled “MULTI-DEVELOPMENT SYSTEM PRINT ENGINE”, byMartin E. Banton;

U.S. application Ser. No. 11/359,065 (Attorney Docket 20051624-US-NP),filed Feb. 22, 2005, entitled “MULTI-MARKING ENGINE PRINTING PLATFORM”,by Martin E. Banton;

U.S. application Ser. No. 11/363,378 (Attorney Docket 20051536-US-NP),filed Feb. 27, 2006, entitled “SYSTEM FOR MASKING PRINT DEFECTS”, byAnderson, et al.;

U.S. application Ser. No. 11/364,685 (Attorney Docket 20051434-US-NP),filed Feb. 28, 2006, entitled “SYSTEM AND METHOD FOR MANUFACTURINGSYSTEM DESIGN AND SHOP SCHEDULING USING NETWORK FLOW MODELING”, byHindi, et al.;

U.S. application Ser. No. 11/378,046 (Attorney Docket 20051682-US-NP),filed Mar. 17, 2006, entitled “PAGE SCHEDULING FOR PRINTINGARCHITECTURES”, by Charles D. Rizzolo, et al.;

U.S. application Ser. No. 11/378,040 (Attorney Docket 20050458-US-NP),filed Mar. 17, 2006, entitled “FAULT ISOLATION OF VISIBLE DEFECTS WITHMANUAL MODULE SHUTDOWN OPTIONS”, by Kristine A. Gerrnan, et al.;

U.S. application Ser. No. 11/399,100 (Attorney Docket 20051634-US-NP),filed Apr. 6, 2006, entitled “SYSTEMS AND METHODS TO MEASURE BANDINGPRINT DEFECTS”, by Peter Paul;

U.S. application Ser. No. 11/403,785 (Attorney Docket 20051623-US-NP),filed Apr. 13, 2006, entitled “MARKING ENGINE SELECTION”, by Martin E.Banton et al.;

U.S. application Ser. No. 11/417,411 (Attorney Docket 20051604-US-NP),filed May. 4, 2006, entitled “DIVERTER ASSEMBLY, PRINTING SYSTEM ANDMETHOD ”, by Paul J. Degruchy;

U.S. application Ser. No. 11/432,993 (Attorney Docket 20050732-US-NP),filed May. 12, 2006, entitled “TONER SUPPLY ARRANGEMENT”, by David G.Anderson;

U.S. application Ser. No. 11/432,924 (Attorney Docket 20050908-US-NP),filed May. 12, 2006, entitled “AUTOMATIC IMAGE QUALITY CONTROL OFMARKING PROCESSES”, by David J. Liebernan;

U.S. application Ser. No. 11/432,905 (Attorney Docket 20050869-US-NP),filed May. 12, 2006, entitled “PROCESS CONTROLS METHODS AND APPARATUSESFOR IMPROVED IMAGE CONSISTENCY”, by Michael C. Mongeon et al.;

U.S. application Ser. No. 11/474,247 (Attorney Docket 20051590-US-NP),filed Jun. 23, 2006, entitled “CONTINUOUS FEED PRINTING SYSTEM”, bySteven R. Moore;

U.S. application Ser. No. 11/483,747 (Attorney Docket 20051806-US-NP),filed Jul. 6, 2006, entitled “POWER REGULATOR OF MULTIPLE MARKINGENGINES”, by Murray O. Meetze, Jr.;

U.S. application Ser. No. 11/485,870 (Attorney Docket 20051681-US-NP),filed Jul. 13, 2006, entitled “PARALLEL PRINTING SYSTEM”, by Steven R.Moore;

U.S. application Ser. No. 11/487,206 (Attorney Docket 20060026-US-NP),filed Jul. 14, 2006, entitled “BANDING AND STREAK DETECTION USINGCUSTOMER DOCUMENTS”, by Wencheng Wu, et al.;

U.S. application Ser. No. 11/495,017 (Attorney Docket 20051521-US-NP),filed Jul. 28, 2006, entitled “SYSTEM AND METHOD FOR PARTIAL JOBINTERRUPT OF NORMAL ORDER OF JOB QUEUE OF MARKING SYSTEMS”, by Lloyd F.Bean, II;

U.S. application Ser. No. 11/501,654 (Attorney Docket 20051001-US-NP),filed Aug. 9, 2006, entitled “METHOD FOR SPATIAL COLOR CALIBRATION USINGHYBRID SENSING SYSTEMS”, by Lalit Keshav Mestha et al.

U.S. application Ser. No. ______ (Attorney Docket 20051335-US-NP), filedSep. 15, 2006, entitled “FAULT MANAGEMENT FOR A PRINTING SYSTEM”, byMeera Sampath, et al.

BRIEF DESCRIPTION

The present disclosure provides a printing device comprising a sheetbuffer including a paper path having a plurality of nip pairs forselectively receiving and releasing a plurality of printer sheets. Theplurality of nip pairs include a fixed load nip pair, a fixed unload nippair, and at least another intermediate fixed nip pair therebetween. Ina first operation each subsequent sheet of the plurality of sheets isshingled over a previous sheet wherein the plurality of sheets can bestopped in the intermediate nip pair or pairs. Individual sheets of theplurality of sheets can be advanced to the unload nip pair sequentiallyin a second operation whereupon the individual sheets are successivelyunloaded as needed in a first in first out order.

The present disclosure further provides for a printing device comprisinga sheet buffer including a paper path having a plurality of nip pairsfor selectively receiving and releasing a plurality of printer sheets.The plurality of nip pairs can include a load nip pair, a release nippair, and at least a first translating nip pair therebetween capable ofhandling a plurality of sheet sizes. In a first position each subsequentsheet of the plurality of sheets can be shingled over a previous sheetwherein the plurality of sheets can be stopped in the translating nippair. The plurality of shingled sheets can be translated together by thetranslating nip pair moving a distance from the first position to asecond position wherein a lead edge of a first or bottommost printersheet is positioned for engagement with the release nip pair.

The present disclosure still further provides for a printing devicecomprising a sheet buffer including a paper path having a plurality ofnip pairs for selectively receiving and releasing a plurality of printersheets. The plurality of nip pairs include a fixed load nip pair, afixed center nip pair, and a fixed unload nip pair. The plurality of nippairs further include at least a first and a second releasable nip pair,the first nip pair between the load nip pair and the center nip pair andthe second nip pair between the unload nip pair and the center nip pair.Each subsequent sheet of the plurality of sheets is shingled over aprevious sheet wherein the first and second releasable nip pairs can beselectively releasable for loading and unloading different size printersheets in a first in first out order in the sheet buffer.

And still further, the present disclosure provides for a printing devicecomprising a sheet buffer including a paper path having a plurality ofnips for selectively receiving and releasing a plurality of printersheets. The plurality of nips including a load group of nips and anunload group of nips. The load group including at least two nip pairsand the unload group including at least two nip pairs. Within each ofthe groups, an intermediate nip pair selectively translates from a firstposition to a second position with respect to the other nip pairs toaccommodate various sheet lengths. One of the nip pairs of each groupcan include at least one fixed nip pair. Within each groups at least theintermediate nip pair is selectively releasable wherein each subsequentsheet entering the sheet buffer shingles over a previously entered andwithin each group the intermediate nip pair selectivlely opens andcloses to insert, hold, and release the sheets.

Further still, the present disclosure provides a printing devicecomprising a sheet buffer including a paper path having a plurality ofnip pairs for selectively receiving and releasing a plurality of printersheets. The plurality of nip pairs include a fixed load nip pair, afixed unload nip pair, and at least another intermediate fixed nip pairtherebetween. In a first operation each subsequent sheet of theplurality of sheets can be overlapped over a previous sheet wherein theplurality of sheets can be stopped between a span defined by the loadnip pair and a next succeeding nip pair. The individual sheets of theplurality of sheets are advanced to the unload nip pair sequentially ina second operation whereupon said individual sheets are successivelyunloaded as needed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic elevational view of a portion of a paper transportsystem according to a first embodiment;

FIG. 2 is another variation of a portion of a paper transport systemaccording to the first embodiment;

FIGS. 3-5 are schematic elevational views of a portion of a papertransport system showing a possible sequence of nip positions accordingto a second embodiment;

FIG. 6 is a schematic elevational view of a portion of a paper transportsystem according to a third embodiment; and,

FIG. 7 is a schematic elevational view of a portion of a paper transportsystem according to a fourth embodiment.

DETAILED DESCRIPTION

The sheet buffer transports, to be described below, can be combined witha plurality of Image Marking Engines (IME). The IMEs can be, forexample, any type of ink-jet printer, an electrophotographic printer, athermal head printer that is used in conjunction with heat sensitivepaper, or any other apparatus used to mark an image on a substrate. TheIMEs can be, for example, black only (monochrome) and/or color printers.Any number of varieties, types, alternatives, quantities, andcombinations of IMEs can be used within the scope of the exemplaryembodiments. It is to be appreciated that, each of the IMEs can includean input/output interface, a memory, a marking cartridge platform, amarking driver, a function switch, a controller and a self-diagnosticunit, all of which can be interconnected by a data/control bus. Each ofthe IMEs can have a different processing speed capability.

Each marking engine can be connected to a data source over a signal lineor link. The data source provides data to be output by marking areceiving medium. In general, the data source can be any of a number ofdifferent sources, such as a scanner, a digital copier, a facsimiledevice that is suitable for generating electronic image data, or adevice suitable for storing and/or transmitting the electronic imagedata, such as a client or server of a network, or the internet, andespecially the worldwide web. The data source may also be a data carriersuch as a magnetic storage disk, CD ROM, or the like, that contains datato be output by marking. Thus, the data source can be any known or laterdeveloped source that is capable of providing scanned and/or syntheticdata to each of the marking engines.

The link can be any known or later developed device or system forconnecting the image data source to the marking engine, including adirect cable connection, a public switched telephone network, a wirelesstransmission channel, a connection over a wide area network or a localarea network, a connection over an intranet, a connection over theinternet, or a connection over any other distributed processing networkor system. In general, the link can be any known or later developedconnection system or structure usable to connect the data source to themarking engine. Further, it should be appreciated that the data sourcemay be connected to the marking engine directly.

In integrated printing architectures comprising multiple markingengines, there is a need for extremely reliable sheet buffers to removeprinter sheet exit time variations and synchronize the printer exitvelocity with the highway timing and velocity, and buffer sheets inarchitectures with mixed printers, e.g. black/white and color printersto achieve efficient printer utilization and maximum system throughput.It is possible to achieve the goals described above with relativelysmall buffers, i.e. a buffer capacity of several sheets is enough. Thepresent disclosure provides a buffer that is extremely reliable by usingonly standard paper path components, for example, nips, nip releases andbaffles.

The present disclosure provides a method and apparatus for bufferingsheets at the output of a printer engine by overlapping or shinglingsheets within an output path prior to delivery to a sheet transporthighway. This allows the print engine to print in advance, store, andthen deliver the sheets on demand into the job matrix. The bufferingconcept can utilize a standard type paper path transport assemblywithout the need of nip release or friction devices to separate thesheets.

The four basic operations of the buffer can be summarized as follows:insert overlapping sheets into buffer stack, hold stack, exit sheet frombuffer stack, and advance stack. As an example, FIGS. 1 and 2 show theoperation of a multiple sheet buffer. For a larger sheet length buffer,the left and right groups of nips can be expanded with adjacent nipsspaced a distance of delta(x) apart.

Referring now to FIG. 1, the buffer apparatus provides for physicallycontrolling the previous sheet's trail edge for initial overlap loadingand independent drives on the nips following the load point. Drive nipsthrough the middle of the overlapping buffer can be drive coupled,however the load sequence may be altered to release a sheet unless thebuffer was already filled to capacity. Overlap loading can be done on astraight paper path, although it is to be appreciated that a humpfeature, bail, or vacuum can be incorporated to control a precedingtrail edge of a sheet. The amount of sheet overlap SO, for oneimplementation, can be defined by an amount less than the nip spacing NSto allow for sheet decoupling at the load and release points. Overlappedsheets S1, S2, S3, and S4 can be stopped in transport, with a previoustrail edge TE of, for example, S4 held below the nip entrance while anext sheet S5 is driven forward into the buffer creating overlap.Subsequently, all of the sheets advance forward to load and accept thenext sheet. The first sheet S1 in the buffer can be ready for release atany time. The sheets can be simultaneously loaded and released at anytime up to buffer capacity without any nip release mechanism. Longersheets can be coupled to multiple nips within the buffer series, but canremain uncoupled for load and release. The aforementioned results inapproximately two times the storage capacity over linear cascadedstorage for 8.5×11 inch size paper across the buffered length. It is tobe appreciated that the aforementioned buffering concept providessimplicity and reliability at a very low cost. The described buffermethod and apparatus can also be extended to finisher applications. Thepaper path transport can be curved (not shown) to allow for sheetoverlap creation at any nip location and allow the buffer to be eitherfront or rear loaded for greater flexibility.

In yet a further embodiment, the present disclosure proposes a methodand apparatus for buffering sheets at the output of a printer engine byoverlapping sheets within its output path prior to delivery to a sheettransport highway. This allows the print engine to print in advance,store, and then deliver the sheets on demand into the job matrix. Thebuffering concept utilizes a sheet loading nip zone whereby the previoussheet's trail edge can be controlled for initial overlap loadingallowing the next or subsequent sheet to be fed over the top of theprevious one. A buffering center or intermediate nip can incrementallycollect a plurality of sheets as they are received in a controlledshingled orientation. The sheet buffer can then hold and control thestack while operating in conjunction with an unloading nip toindividually separate and release the shingled sheet stack as the sheetsare required into the job matrix. The buffer can utilize standardtransport nip components without the need for nip release or frictiondevices to separate the sheets. The amount of sheet overlap can bemaximized (regardless of paper length) while limiting the minimumshingle offset needed to independently transfer control of the incomingor outgoing sheet between nips. The shingle device can offer up toapproximately 10× the storage capacity for large sheets over linearcascading of sheets across the transport length. The buffering methodoffers large buffering capacity limited by the minimum required shinglelength divided into the sheets length with minimal complexity. Theloading nip can be closely coupled to part of the print engine since itcan run continuously at constant velocity.

In the drawings, like reference numerals have been used throughout todesignate identical elements. FIG. 2 schematically depicts a portion ofa sheet transport system having a sheet buffering arrangement accordingto the disclosure incorporated therein. The system shown in FIG. 2 isintended for use in an electrophotographic printing machine; however,the apparatus and system could clearly be used in a variety of othertypes of equipment incorporating sheet handling and transportationsystems. Broadly, as illustrated in FIG. 2, the apparatus generallycomprises guide means which define a predetermined course of papermovement or path indicated generally by the line P. The guide meanscomprise a spaced pairs of respective upper and lower guide panels (notshown), respectively, which direct sheets to a first pair ofhorizontally positioned driven rolls 16 and 18, respectively. The rolls16 and 18 are positioned on each side of path P and driven in thedirection of the arrows to define a first drive nip 20.

The buffering station 24 is located immediately downstream of the driverolls 16, 18 and includes upper and lower sheet guides 26 and 28 whichare positioned in spaced opposed relationship and arranged to directsheets coming from the drive nip 20 downwardly into the nip 30 of asecond pair of spaced rolls 32 and 34, respectively.

Sheets passing through the nip 30 are received and directed along thepredetermined path of paper movement to subsequent use or processingequipment (not shown) by suitable guide means in the form of guideplates or panels 36 and 38.

The rolls 32 and 34 can be a standard driver and idler nip pair or eachcan be provided with drive means capable of uniform operation forimproved buffer stack control. The drive means can comprise any standardtype of drive motor. Although not illustrated, roll 34 can be providedwith a first independent drive means. Roll 32 can be a simple idler orcan be driven in a similar manner from another independent or gangeddrive means. The drive means can be controlled from a main controllerunit. Suitable sheet sensors 17 and 19 can be positioned just downstreamof the rolls 16 and 18 to detect the lead edge and trail edge of sheetsentering the buffering station 24.

The system and apparatus shown in FIG. 2 allows one or more sheets to bestopped in the buffering station 24 and held in nip 30 and thenincrementally transferred downstream into a nip 40 of a third pair ofspaced rolls 42, 44. While this function is being carried out, thesystem maintains a positive drive on the sheets at all times. The systemcan be configured so that the driven rolls of 32 and/or 34 have asufficient coefficient of friction relative to the paper being handled.Multiple sheet interfaces are controlled by applying sufficient normalforce within nip 30 and relying on sheet to sheet coefficient offriction to advance the plurality of sheets in unison.

In operation a first buffered sheet can be driven into the buffering nip30 by being directed thereto from rolls 16 and 18. At the time the sheetcan be directed into the buffering nip 30 which is being driven from itsrespective drive means. As the trailing edge of the sheet passes thesensors 17, 19, the controller acts to stop the driving movement of nip30.

It should be noted as shown in FIG. 2 (and illustrated in FIG. 3) thatwhen the sheet has moved to the stopped position, the trailing edge canbe in a position slightly behind roll 18. This places the first sheet'strail edge in a position such that the second sheet to enter thebuffering station 24 from rolls 16, 18 will enter at a position abovethe first stopped sheet and advance forward into the buffer station 24creating overlap with the previous sheet. As the second sheet approachesnip 30, the nip 30 drive means is once again engaged to advance thefirst sheet along with the second sheet until the trail edge of thesecond sheet is seen at sensors 17 and 19. Drive nip 30 is then stoppedagain and the buffer is ready to receive the next consecutive orsubsequent sheet. The aforementioned is shown in FIG. 2 wherein theconsecutive sheets entering the buffer are engaged between the firstsheet SI and roller 32 in an incremental shingled orientation. With thedesired sheets loaded into the buffered stack of nip 30, nip 30 can beincrementally actuated on demand to drive sheets S1, S2, and all otherremaining sheets out of the stack and into nip 40 to exit the bufferingstation 24 in first in first out sequential order. It is to beappreciated that nip 30 can be stopped for any predetermined period oftime to hold buffered sheets within the buffer 24 for delivery asrequired.

It is to be appreciated that the single set of drive rolls incombination with superposed idler rolls can hold a first sheet while asecond, third, fourth, fifth, sixth, etc. sheet is driven into the nipbetween the driven and idler rolls. More particularly, as illustrated,the set of opposed rolls 16 and 18, defining a feed nip 20, can bedriven in the direction shown to feed paper sheets S1-S6 along the paperpath 58 to the buffering station 24.

The buffering station 24 can include support and guide baffles toconfine the sheets moving along the paper path and direct them into theroll arrangement 42, 44. The roll arrangement 42, 44 comprise rolls thatare driven from a suitable drive.

In operation, the first sheet S1 to enter the buffering station 24 isstopped at the location shown by sheet S6, by stopping the drive nip 30.These rolls can have a high coefficient of friction. The first sheet S1is thus held in the position while the next sheet S2 enters thebuffering station.

When the second sheet S2 is appropriately shingled with sheet S1, thecontroller actuates the drive rolls of nip 30. Both sheets S1 and S2 arethen advanced through the nip since sheet S2 is loaded against sheet S1by the roll 32. This generates a positive drive force on both sheets.

It is to be appreciated that the paper handling system provides for aset of individual documents to be maintained partially separated, butpartially overlapping, during their buffering. The disclosure providesfor the use of paper path elements, for example, nips, nip releases andbaffles. Sheets can be buffered by storing them shingled relative toeach other by a distance delta(s) apart in the process direction. Groupsof nips, both comprising several nips, can be located at the entry ofthe buffering zone (i.e. entrance nip groups) and at the exit of thebuffering zone (i.e. exit nip groups). The nips between each group canbe spaced a distance of delta(x) apart. The operation of nips in eachgroup can be coordinated to perform the “insert sheets into buffer”,“hold sheets” and “feed out sheets from buffer” operations. The sheetscan be stored shingled in the buffer by the buffering nip grouppositioned in between the entrance and exit nip groups. The insertionand feed out operations can be performed on each sheet independentlyfrom the other sheets. Appropriate point sensors at the buffer entranceand exit, together with feedback control of sheets and nips ensure theproper position control of all sheets entering and exiting the buffer,as well as the sheets inside the buffer.

Referring now to FIGS. 3-5, another buffer 124 is therein shown whichcan hold sheets of the same size at any given time, but can switch sizesif emptied out first. The buffer 124 can consist of three groups ofnips, one at the entrance 116, 118, one at the exit of the buffer 142,144, and one therebetween 132, 134. Each group includes a nip 120, 130,140, a variable distance apart. To be described in more detail below,the nip 130 is capable of translating. Sheets are held shingled in thebuffer by nip 130 positioned between nips 120 and 140.

Referring again to FIGS. 3-5, the entrance or loading nip pair 116, 118,the translating or intermediate nip pair 132, 134, and the exit orrelease nip pair 142, 144 are therein shown. It is to be appreciatedthat the distance between the loading nip pair 116, 118 and thetranslating nip pair 132, 134, when the translating nip pair 132, 134 isin the load position (FIG. 3), is slightly less than the sheet length.The translating nip pair 132, 134 can translate from a first position toa second position. The second position for the translating nip pair isreferenced 132′, 134′.

Once the shingled sheets are loaded, the translation nip 130 holds theshingled sheets and translates them forward (FIG. 4) such that theleading edge 160 of a first or bottom sheet S1 is ready to engage withthe release nip 140 (FIG. 5). As the buffered sheets S1, S2, S3, S4, S5are needed or desired for the job set, the translating and release nips130, 140 drive the shingled stack forward until the trail edge 162 ofthe first sheet S1 is released and under the control of the release orunload nip 140.

The translation of the ‘center’ nip pair 132, 134 is implemented for thepurpose of buffering with multiple sheet lengths. It is to beappreciated that for a single sheet length the ‘center’ nip pair 132,134 can be fixed and spaced appropriately from the load 116, 118 andrelease 142, 144 nip pairs as illustrated in FIG. 2.

Sheet buffer capacity can be increased by ganging additional nips 230,231 (refer to FIG. 6) within the translation or fixed assembly of abuffer 224 on a common drive. This increases the existing capacity bysubstantially the total nip span divided by the minimum shingle distancewithout any need for nip releases. Also, the holding grip on theshingled stack at nips 230, 231 is increased for better positioncontrol. The entrance or loading nip pair 216, 218, the translating orintermediate nips 230, 231, and the exit or release nip pair 242, 244are shown in FIG. 6. It is to be appreciated that the distance betweenthe loading nip pair 216, 218 and the adjacent fixed or translating nippair 232, 234, when the fixed or translating nip pair 232, 234 is in theload position, is slightly less than the sheet length. The translatingnip pairs 232, 234 and 233, 235 can translate from a first position to asecond position. The second position for the translating nip pairs isnot illustrated. Once the shingled sheets are loaded, the translationnips 230, 231 hold the shingled sheets and translate them forward suchthat a leading edge 260 of a first or bottom sheet S1 is ready forengagement with the release nip 240. As the buffered sheets S1, S2, S3,S4, S5 are needed or desired for the job set, the translating andrelease nips 230, 231, 240 drive the shingled stack forward until thetrail edge 262 of the first sheet S1 is released and under the controlof the release or unload nip 240. Buffering of different media sheetsizes can be accommodated by positioning the entrance and exit nipsaccurately with respect to the intermediate center nips. The entrancenips, intermediate nips, and/or exit nips can be moveable andincorporate additional spanner nips in order for the buffer toaccommodate media of different sizes.

Preventing stubbing at the buffer entrance is desirable. Sheets withup-curl or down-curl can present a problem as they enter the buffer. TheLE of the entering sheet may stub on the TE of sheets already in thebuffer. To minimize this risk, a slight curve that pushes down the TE ofthe sheets already in the buffer can be designed into the baffles. Also,the nips in the entrance nip group can be tilted to help guide theentering LE over the trail edge of the previous buffered stack.

In yet a further embodiment, the present disclosure proposes a methodand apparatus for buffering sheets at the output of a printer engine byoverlapping sheets within its output path prior to delivery to a sheettransport highway. This allows the print engine to print in advance,store, and then deliver the sheets on demand into the job matrix. Thebuffering concept can utilize a sheet-loading nip zone whereby theprevious sheet's trail edge can be controlled for initial overlapshingle loading allowing the next sheet to be fed over the top of theprevious one. A fixed buffer center nip with additional intermediate nippairs located on each side of that center nip can be arranged. Theseintermediate nip pairs can be positioned and oriented for various sheetlength requirements and equipped with nip release mechanisms. The closedor acting nip pairs along with the center nip incrementally collect aplurality of sheets as they are received in a controlled shingledorientation. They hold and control the stack and then operate inconjunction with an unloading nip to separate and individually releasethe shingled sheets, as they are required into the job matrix. Thebuffer can utilize standard transport nip components without the needfor friction devices to separate the sheets. The amount of sheet overlapis maximized (regardless of paper length) and limited only to theminimum shingle offset needed to independently transfer control of theincoming or outgoing sheet between nips. The shingle device can offer upto approximately 10× the storage capacity over linear cascading ofsheets across the transport length. The buffering method offers largebuffering capacity limited by the minimum required shingle lengthdivided into the sheet length plus the total span of acting intermediatenips. The loading nip can be closely coupled or part of the print enginesince it can run continuously at constant velocity.

Referring now to FIG. 7, multiple sheet lengths can be buffered byreplacing translating nips with multiple nip pairs 352, 354; 356, 358;332, 334; 372, 374; 376, 378 positioned and oriented for various lengthrequirements between the load 316, 318, center 332,334 and unload 342,344 nip pairs. The multiple nips 350, 351, 370, 371 can include niprelease mechanisms for selective opening of one or more nip pairs (FIG.7). For small size sheets nips 350, 351,370, 371 would remain closed.For medium size sheets nips 350, 371 would open while nips 351, 370would remain closed. For large size sheets nips 350, 351,370, 371 wouldremain open. Additional nip pairs can be added or the nips can betranslated as needed for expanded sheet size requirements.

And still further, the present embodiment provides for a printing devicecomprising a sheet buffer including a paper path buffer having aplurality of nips for selectively receiving and releasing a plurality ofprinter sheets. Referring again to FIG. 7 with the omission of thecenter nip, the plurality of nips including a load group of nips320,350,351 and unload group of nips 370,371,340. The load groupincluding at least two nip pairs and the unload group including at leasttwo nip pairs. Within each of the groups, the intermediate nip pairs350,351,370,371 can remain fixed or translate from a first position to asecond position with respect to the other nip pairs 320, 340 toaccommodate various sheet lengths. The rightmost and leftmost nip pairsof each group can include at least one fixed nip pair. The intermediategroup of nips are releasable wherein after a first plurality of sheetsentering the sheet buffer are shingled over the previous sheets, the nippairs can open and close to perform an insert, hold and release functionon the shingled stack.

It is to be appreciated that any of the described buffers can be coupledserially or in parallel to increase the buffering capacity. And any ofthe described buffers can be coupled to a parallel path for bypass orleapfrogging of a sheet ahead of another. The described method andembodiments can also be extended to finisher or other applications.

While the present printing apparatus and method has heretofore beendescribed in connection with exemplary embodiments, it will beunderstood that it is not intended to limit the embodiments. On thecontrary, it is intended to cover all alternatives, modifications andequivalents as may be included within the spirit and scope of theembodiments as defined by the appended claims.

1. A printing device comprising: a sheet buffer including a paper pathhaving a plurality of nip pairs for selectively receiving and releasinga plurality of printer sheets; said plurality of nip pairs including afixed load nip pair, a fixed unload nip pair, and at least anotherintermediate fixed nip pair therebetween; in a first operation eachsubsequent sheet of said plurality of sheets is shingled over a previoussheet wherein said plurality of sheets are stopped in said intermediatenip pair; and, individual sheets of said plurality of sheets areadvanced to said unload nip pair sequentially in a second operationwhereupon said individual sheets are successively unloaded as needed. 2.The printing device of claim 1, wherein said plurality of sheets are ofthe same size.
 3. The printing device of claim 2, wherein said sizeincludes a length, said length is greater than a spacing defined betweenadjacent nip pairs.
 4. The printing device of claim 1, whereinsuccessive unloading occurs in a first in first out order from saidsheet buffer.
 5. The printing device of claim 1, wherein said secondoperation is downstream form said first operation.
 6. A printing devicecomprising: a sheet buffer including a paper path having a plurality ofnip pairs for selectively receiving and releasing a plurality of printersheets; said plurality of nip pairs including a load nip pair, a releasenip pair, and at least a first translating nip pair therebetween; in afirst position each subsequent sheet of said plurality of sheets isshingled over a previous sheet wherein said plurality of sheets arestopped in said translating nip pair; and, said plurality of shingledsheets are translated together by said translating nip pair moving adistance from said first position to a second position wherein a leadedge of a bottommost printer sheet is positioned ready for engagementwith said release nip pair.
 7. The printing device of claim 6, whereinsaid first position is a load position and said second position is anunload position whereupon said sheets are successively unloaded fromsaid second position as needed.
 8. The printing device of claim 7,wherein said second position is downstream from said first position. 9.The printing device of claim 6, wherein said translating from said firstposition to said second position including maintaining said translatingnip pair in a closed position wherein all said plurality of shingledsheets move together from said first position to said second position.10. The printing device of claim 9, wherein said plurality of sheets isat least one sheet.
 11. The printing device of claim 9, wherein saidplurality of sheets is at least two sheets
 12. The printing device ofclaim 9, wherein said distance is based on a first length of saidplurality of sheets and another distance is based on a second length ofsaid plurality of sheets.
 13. The printing device of claim 9, whereinsaid distance is selectable and based on a length of said plurality ofsheets.
 14. The printing device of claim 9, wherein said load nip pairand said release nip pair are fixed in said paper path.
 15. The printingdevice of claim 9, wherein a selected number of said plurality of sheetsare loaded prior to translating from said first position to said secondposition.
 16. The printing system of claim 7, wherein successiveunloading occurs in a first in first out order from said sheet buffer.17. The printing system of claim 6, wherein said paper path is curvedbetween said load nip pair and said first translating nip pair.
 18. Theprinting system of claim 6, further including a second translating nippair, said first translating nip pair and said second translating nippair translate together in tandem.
 19. The printing system of claim 6,further including a plurality of translating nip pairs, said pluralityof translating nip pairs translate together in tandem.
 20. The printingsystem of claim 6, further including a plurality of translating nippairs, wherein the spacing between adjacent nip pairs is variable; and,a maximum distance between adjacent nip pairs is less than said sheetlength.
 21. The printing system of claim 6, further including aplurality of translating nip pairs, wherein the spacing between adjacentnip pairs is fixed and less than said sheet length.
 22. The printingsystem of claim 6, wherein the spacing between said first translatingnip pair and said load nip pair is smaller than said sheet length insaid first position.
 23. The printing system of claim 6, wherein thespacing between said last translating nip pair and said release nip pairis less than said sheet length in said second position.
 24. The printingsystem of claim 23, wherein the spacing between said first translatingnip pair and said load nip pair is less than said sheet length in saidfirst position.
 25. The printing device of claim 6, further including arange for said distance wherein said range is based on difference insize between a smallest and largest selected sheet.
 26. A printingdevice comprising: a sheet buffer including a paper path having aplurality of nip pairs for selectively receiving and releasing aplurality of printer sheets; said plurality of nip pairs including afixed load nip pair, a fixed center nip pair, and a fixed unload nippair; said plurality of nip pairs further including at least a first anda second releasable nip pair, said first nip pair between said load nippair and said center nip pair and said second nip pair between saidunload nip pair and said center nip pair; and, each subsequent sheet ofsaid plurality of sheets is shingled over a previous sheet wherein saidfirst and second nip pairs selectively releasable for loading andunloading a first size printer sheet in a first in first out order insaid sheet buffer.
 27. The printing device of claim 26, said pluralityof nips further including at least a third and a fourth releasable nippair, said third nip pair between said load nip pair and said first nippair and said fourth nip pair between said unload nip pair and saidsecond nip pair wherein each subsequent sheet of said plurality ofsheets is shingled over a previous sheet wherein said third and fourthnip pairs selectively releasable for loading and unloading a second sizeprinter sheet in a first in first out order within a buffering zone. 28.The printing device of claim 27, wherein said first size printer sheetis larger than said second size printer sheet.
 29. The printing deviceof claim 27, wherein a number of nip pairs between said load nip pairand said unload nip pair is equivalent to said plurality of sheet sizerequirements in said buffering zone.
 30. The printing system of claim26, wherein each sheet includes a selectable length; and, a spacing isdefined between said load nip pair and said unload nip pair wherein saidspacing is less than two times the maximum sheet length.
 31. A printingdevice comprising: a sheet buffer including a paper path having aplurality of nips for selectively receiving and releasing a plurality ofprinter sheets; said plurality of nips including a load group of nipsand an unload group of nips; said load group including at least two nippairs and said unload group including at least two nip pairs; withineach said group an intermediate nip pair selectively translates from afirst position to a second position with respect to the other nip pairsto accommodate various sheet lengths; one of the nip pairs of each saidgroup includes at least one fixed nip pair; within each said group atleast said intermediate nip pair selectively releasable; and, whereineach subsequent sheet entering said sheet buffer shingles over apreviously entered sheet, and within each said group said intermediatenip pair selectively opens and closes to insert, hold, and release saidsheets.
 32. The printing device of claim 31, wherein said intermediatenips selectively translate from said first position to said secondposition for accommodating a second size sheet.
 33. The printing systemof claim 31, wherein said intermediate nips selectively translate fromsaid first position to a third position to accommodate another sizesheet.
 34. A printing device comprising: a sheet buffer including apaper path having a plurality of nip pairs for selectively receiving andreleasing a plurality of printer sheets; said plurality of nip pairsincluding a fixed load nip pair, a fixed unload nip pair, and at leastanother intermediate fixed nip pair therebetween; in a first operationeach subsequent sheet of said plurality of sheets is overlapped over aprevious sheet wherein said plurality of sheets are stopped between aspan defined by said load nip pair and a next succeeding nip pair; and,individual sheets of said plurality of sheets are advanced to saidunload nip pair sequentially and then successively available forunloading as needed.
 35. The printing device of claim 34, wherein saidplurality of sheets are of the same size.
 36. The printing device ofclaim 35, wherein said size includes a length, said length is greaterthan a spacing defined between adjacent nip pairs.
 37. The printingsystem of claim 35, wherein each pair of adjacent sheets includes anamount of overlap and each adjacent nip pairs include a spacingtherebetween, said overlap is less than said spacing in said bufferingzone.
 38. The printing device of claim 34, wherein said intermediate nippair is said unload nip pair.
 39. The printing device of claim 35,wherein said plurality of nip pairs in said sheet buffer corresponds tosaid plurality of sheets in said sheet buffer.